Add content description to ButtonInfo for accessibility

This allows TalkBack to announce a message different from the button's
visible text. It enhances accessibility by providing more contextual or
descriptive information for screen reader users.

Flag: EXEMPT bugfix
Bug: 419160629
Test: manually test with TalkBack on, screenshots attached in bug
Change-Id: I0072a5c52e3e26f7691eec7207e72aefa88604f5